Electrodeposition, although known for some time, has only recently become of commercial importance as a coating application method. While many compositions can be electrodeposited, most coating compositions when applied using electrodeposition techniques do not produce commercially usable coatings. Moreover, electrodeposition of many coating materials, even when otherwise successful, is attended by various disadvantages, such as non-uniform coatings and poor throw power. In addition, the coatings obtained are, in most instances deficient in certain properties essential for their utilization in many applications. In particular, properties such as corrosion resistance and alkali resistance are difficult to achieve with resins conventionally employed in electrodeposition processes. Likewise, staining and yellowing on baking or aging are problems which must be met to produce a commercially-successful resin for many applications. Anionic resins, due to their acidic nature, tend to be sensitive to common types of corrosive attack, for example, salts and alkalis. Many electro-depositable anionic coatings are subject to discoloration or staining because of dissolution of metal ions at the anode which is being coated.
Epoxy resins are among the most useful resins for many purposes and have excellent corrosion resistance and other properties. They are employed in many coatings, but have not been employed in water-dispersible compositions suitable for application by electrodeposition because they cannot be adequately dispersed in water under the conditions required in such processes. Esterified epoxies have been utilized, but these act similarly to the polycarboxylic acid resins, and while offering many advantages over such polycarboxylic acid resins, are still subject to many of their disadvantages.
Recently, there has been developed a group of water-dispersible, quaternary ammonium salt-containing resins which have utility as coating resins in general, and particularly, in aqueous electrodepositable compositions.
These resins are prepared by reacting an epoxy-group containing organic material, preferably a resin which is a polyepoxide containing a plurality of epoxy groups with an amine acid salt, yielding a resin preferably containing epoxy groups and contaning quaternary ammonium salt groups.